Method for induced production of petroleum by means of horizontal fractures

ABSTRACT

The present invention relates to a method for produce viscous oil in wells through steam injection into horizontal fractures. The objective of the method is achieved through fracturing operations that form a horizontal fracture being this fracture sustained by a sustaining agent, for example, by a bauxite-type, that is resistant to steam in areas of the well ( 1, 11, 12 ) that reach the oil-producing formation ( 6 ) both in the bottom area ( 61 ) and in the top area ( 62 ). Vapor, associated or not with another fluid, for example, an organic solvent is injected into the producing well ( 1, 11, 12 ) displacing the oil of the formation in a linear manner and through gravity.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon, claims the benefit of, priority of, and incorporates by reference, the contents of Brazilian Patent Application No. PI 0800928-7 filed Apr. 2, 2008.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention concerns the field of methods to increase production in oil-producing wells by means of fracturing and induction of production by means of the injection of fluids at high temperature.

Oil production in general is always concerned with developing techniques for increasing productivity in a producing well, as well as increasing the recovery of oil contained in the reservoir. The incessant search of the art lies in methods that might reduce the viscosity of oil by making a simple form of production viable, which, at the same time, results in fewer costs for an efficient production.

The most utilized effect for boosting the reduction of viscosity in oil is to increase its temperature whereby it becomes less viscous. Methods for increasing oil temperature include: the use of electrical resistance, electromagnetism, ultra-sound, exothermic chemical reactions, “in situ” combustion and steam injection.

With regard to steam injection more specifically, steam can be injected either cyclically or continuously.

In cyclical injection, steam is normally injected into a specific oil-producing formation interval, and, some time later, the interval is brought on stream.

In continuous injection, steam is injected into a specific oil-producing formation interval, normally referred to as the injector well and production occurs through other, near-by wells called producing wells.

One of the steam injection methods known in the art is known by the abbreviation “SAGD” (System Assisted Gravity Drainage). It is applied in many reservoirs that contain highly viscous bitumen. The concepts of this method have already been widely published and discussed extensively in the industrial literature on the art.

The “SAGD” method normally comprises two co-planar horizontal wells, that are vertical, where steam in injected into the upper well and production occurs through the lower one. The system uses a greater area, both for injection and production, since wells are horizontal and extend further into the producing formation than other wells such as vertical wells and diverted wells.

The “SAGD” Method makes use of the injection area that provides a greater area of influence of the steam, which thereby increases oil production.

2. Related Art

There are various documents on the art that explain methods for increasing well productivity and recovery of viscous oil contained in a reservoir.

U.S. Pat. No. 4,175,618 (Texaco Inc.), incorporated herein by reference, discloses a process of thermal recovery of oil using steam injection or hot water to move viscous petroleum by sweeping only a small fraction of the formation between the wells.

U.S. Pat. No. 4,733,726 (Mobil Oil Corporation), incorporated herein by reference, discloses a method for the recovery of oil from an oil-containing subterranean formation by pressurized steam flooding and a production program. During the first phase, steam is injected into the formation and oil is recovered when the steam goes through to the producing well. Next, a pressurization phase is begun to speed up output from the well while injection of the steam continues until the bottom injection pressure is as great as the vertical pressure created by the over load that in turn causes a horizontal fracture in the formation. After the horizontal fracture is formed, a third production phase is begun in which the oil is recovered from the formation through the producing well or the injection well or both, while production as a whole is poor. Also, during the production phase, if the oil is recovered only through the injection well or the producing well, the steam may be injected through the non-producing well, until the amount of recovered oil becomes poor. In this way, the injection, pressurization and recovery phases may be repeated until the production of oil becomes uneconomical.

U.S. Pat. No. 4,889,186 (Comdisco Resources, Inc.), incorporated herein by reference, discloses a method to stimulate the recovery of hydrocarbons as oil from a geological reservoir through an injection well and a plurality of production wells which are extending over the geological reservoir. Flooding is performed through at least one injector well in the lowest part of the geological reservoir to thereby form a horizontal fracture by injection with a vertical component.

U.S. Pat. No. 5,273,111 (Amoco Corporation), incorporated herein by reference, discloses a method that combines movement from the effect of fluid and drainage through gravity for production of hydrocarbons from a subterranean formation, that includes injecting fluid through at least two upper horizontal wells to move the hydrocarbons to, at least, one lower horizontal well through which the hydrocarbons are produced, where each lower horizontal well is laid out laterally and vertically below and between the respective upper wells. The hydrocarbons, produced through the lower horizontal well, have a cumulative rate that is faster than the cumulative rate of fluid injected through the adjacent upper wells.

U.S. Pat. No. 5,626,193 (Elan Energy, Inc.), incorporated herein by reference, discloses a process for recovery of all products from a narrow dimension reservoir via gravity-assisted drainage with only one horizontal well. Steam is injected through a complete tubing or a partially insulated tubing with the exit next to the edge of a long vertical well that penetrates the reservoir of viscous oil. Low quality steam is injected for conditioning and heating in a radius of 1 to 2 meters of the well. Oil and fluids from the immediately adjacent reservoir start to be produced through the annular space of the horizontal well between the insulated tubing and the liner.

U.S. Pat. No. 5,860,475 (Amoco Corporation), incorporated herein by reference, discloses a process for thermal recovery of heavy oil from a reservoir that presents a plurality of laterally spaced vertical wells whose use has made the reservoir, characterized by a heated depletion zone, a drainage channel, mobility or communication channel. The process includes the stages of drilling a well with a horizontal section and an opening therein that is located laterally between at least two of the vertical wells and the part that is lowest in it, at the reservoir bottom; injecting steam through the vertical wells to establish thermal communication with the horizontal well; and utilizing the combination of steam and gravity-induced drainage for the recovery of oil through the horizontal well.

With regard to horizontal wells, or the combination of horizontal and vertical wells that present results and are widely used, as was seen above, should be taken into account not only the problems as regards additional costs and technologies of drilling horizontal wells but also the operational problem involved when the depth of reservoir is shallow. It is still desirable through the present know how an oil production way more efficient, less costly, that would be easy to operate in cases of very shallow reservoirs, and, finally, that could be used for vertical wells that already exist.

SUMMARY OF THE INVENTION

The objective of this invention is a method for a production of viscous oil in wells through steam injection into horizontal fractures.

The method of this invention applies to a new or already existing single well, or to a set of new or already existing laterally spaced wells.

For this invention, all wells are vertical.

The objective of this invention is achieved via fracturing operations to form a horizontal fracture being this fracture sustained by a sustaining agent, for example, bauxite-type sustaining agent, that is resistant to steam in areas of the well that reach the producing formation both in the bottom area and the top area of the well. Steam, associated or not with another fluid, such as an organic solvent, is injected into the producing well and displaces the formation's oil in a linear manner or through gravity.

The following benefits of the method proposed by this invention in view of the art that was presented above may be listed: it eliminates the need to dig one or more expensive, limited-use horizontal wells; greater steam/oil contact area; linear flow of steam in the reservoir; use of the independent method on drilling wells which can be applied to wells already existing; speed of implementation and lower cost in terms of a complete operation involving horizontal wells.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an illustration of applying the method of this invention to a vertical well according to this invention; and

FIG. 2 is an illustration of applying the method of this invention to more than one vertical well according to this invention.

DETAILED DESCRIPTION OF THE INVENTION

This invention refers to a method for the production of viscous petroleum in vertical, petroleum-producing wells through undertaking steam injection and the resulting gravity-induced production utilizing horizontal fractures running the length of the depth of the same well or more than one well in areas that reach the top or bottom area of a producing formation.

The principal benefits that can immediately be perceived with regard to other methods present in the current art are the exemption of drilling horizontal wells at least two, which is extremely costly, and the obtainment of large extension areas determined by the size of fracturing performed.

In the art processes, the flow of steam within the producing formation occurs radially. In the method of this invention, the steam has a linear flow throughout the fracturing area, which provides contact between the steam, increased with or without another fluid, and the oil of the producing formation, resulting in a quality much higher than that of other methods.

This method provides an increase in production and the volume of oil produced via an increase in the recovery factor at a lower cost.

In a practical example and merely illustrative, it can be said that, for a horizontal well with a nine-inch diameter to have the same horizontal fracturing area with a radius of about thirty meters, where only one face of the fracture is considered, this horizontal well would have an extension of about three thousand nine hundred meters in the reservoir. It is a very expensive operation and difficult or even impossible to implement in cases of very shallow reservoirs.

Fracturing normally has lower implementation costs with regard to the construction of horizontal wells.

Fracturing may be programmed for extensions suitable to various situations and the operations may be done in a conventional manner.

The method object of this invention may be accompanied by the help of FIG. 1 and basically includes the following steps to be implemented in a single well (1):

in a vertical well (1), perform a first horizontal hydraulic fracturing (51) at the bottom area (61) of an oil-producing formation (6);

then perform a second horizontal hydraulic fracturing (52) in the same well (1) at the top area (62) of the same oil-producing formation (6);

carry out in the well (1) completion operation by the installation of a double valve (41) through which an injection column (21) and a production column (22) pass in the area above the second fracture (52) and, the installation of single valve (42) through which the production column (22) passes in the area above the first fracture (51) and under the second fracture (52);

inject steam through the injection column (21) into the interior of the second horizontal hydraulic fracture (52); and

recover the oil that has flowed by the first horizontal fracture (51) through the production column (22).

For the purpose of simplification only, in the event of having more than one vertical well (1), a case that shall be presented in the example that follows below, the description will be done for two vertical wells (11, 12), and should not be considered as limited to them.

The method that is the purpose of this invention, in a second embodiment which may be accompanied by the support of FIG. 2, basically includes the following steps when realized in more than one well (1):

in a first vertical well (11), perform a first horizontal, hydraulic fracturing (51) in the bottom area (61) of an oil-producing formation (6);

in a second vertical well 12, perform a second, horizontal hydraulic (52) fracturing in the top area (62) of the same oil-producing formation (6);

perform a well completion operation in the first well (11) by installation of a single valve (42) through which a production column (22) passes in the area above the first fracturing (51);

perform a second well (12) completion operation by installation of a single valve (42) through which an injection column (21) passes in the area above the second fracture (52);

inject steam through the injection column (21) of the second well (12) to the interior of the second horizontal hydraulic fracture (52); and

recover the oil flowed by the first horizontal fracture (51) through the production column (22) of the first well (11).

Vertical wells (1, 11, 12) may be new wells or already drilled wells.

Steam injection in the interior of the second fracture (52) can be choosing by: steam injection only; injection of steam with production boosting fluids; steam cyclical injection; and steam continuous injection.

In the second horizontal hydraulic fracture (52) into the interior of which the steam is injected, the pressure is greater than the one of the first horizontal hydraulic fracture (51) and that is why, the flow of oil is displaced from the second fracture (52) to the first fracture (51).

Though this invention has been described in the preferred manner for undertaking it, the main concept guiding this invention that is a method for production of viscous petroleum in vertical petroleum production wells through operation of steam injection and resulting production through gravity using horizontal fractures located along the depths of a same or more than one well in areas that reach the higher part and lower part of the reservoir, retain its innovative character, and on which those versed in the art can foresee and perform variations, modifications, alterations, adaptations, and compatible and appropriate equivalents for the work environment in question, without, overall, distancing themselves from relevance of the spirit and scope of this invention, that are represented by the claims below. 

1. Method for induced production of petroleum by means of horizontal fractures, characterized by the following steps in implementation in a single well: in one vertical well (1) perform an initial horizontal hydraulic fracture (51) in the bottom area (61) of an oil-producing formation (6); then perform another horizontal hydraulic fracture (52) in the same well (1) in the top area (62) of the same oil-producing formation (6); perform a well (1) completion operation with the installation of a double valve (41) through which an injection column (21) and a production column (22) pass in the area above the second fracture (52) and, the installation of a simple valve (42) through which the production column (22) passes in the area above the first fracture (51) and under the second fracture (52); inject steam through the injection column (21) into the second horizontal hydraulic fracture (52); and recover the oil flowing from the first horizontal fracture (51) through the production column (22).
 2. Method for induced production of petroleum by means of horizontal fractures, characterized by the following steps in implementation in more than one well: in a first vertical well (11), perform a first horizontal hydraulic fracture (51) in the bottom area (61) of an oil-producing formation (6); in a second vertical well (12), perform a second horizontal hydraulic fracture (52) in the top area of the (62) same oil-producing formation (6); perform a well completion operation in the first well (11) with the installation of a single valve (42) through which a production column (22) passes in the area above the first fracture (51); perform a well completion operation in the second well (12) with the installation of a single value (42) through which an injection column (21) passes in the area above the second fracture (52); inject steam through the injection column (21) of the second well (12) into the second, horizontal hydraulic (52) fracture; and recover oil flowing from the first, horizontal fracture (51) through the production column (22) of the first well (11).
 3. Method according to claim 1, wherein the vertical wells (1, 11, 12) are new wells.
 4. Method according to claim 2, wherein the vertical wells (1, 11, 12) are new wells.
 5. Method according to claim 1, wherein the vertical wells (1, 11, 12) are existing wells.
 6. Method according to claim 2, wherein the vertical wells (1, 11, 12) are existing wells.
 7. Method according to claim 1, wherein the injection of steam in the interior of the second fracture (52) can be chosen by: steam injection only; steam injection with production-boosting fluids; cyclical steam injection; and continuous steam injection.
 8. Method according to claim 2, wherein the injection of steam into the second fracture (52) can be chosen by: steam injection only; steam injection with production-boosting fluids; cyclical steam injection; and continuous steam injection. 